Nanoindentation response of PZT and NKN-NT piezoceramics

Nanoindentation experiments are carried out on two different piezoceramics, lead zirconate titanate (PZT) and sodium potassium niobium-sodium titanate (NKN-NT) was investigated with an aim to understand the effect of the material (pristine poled vs. annealed unpoled) on the hardness and elastic modulus. Indentations were performed in the peak-load range of 2000 mu N to 4000 mu N. In both the cases PZT exhibits a higher hardness and elastic modulus than NKN-NT. It has also been observed that the hardness of pristine and annealed samples decreases with indentation load indicating a strong indentation size effect. However, the elastic modulus in pristine PZT was found to be load independent. The marked dependency of hardness and elastic modulus on indentation size effects is discussed. A shift in crystal structure was observed in both piezoceramics when annealed above their Curie temperature. Scanning electron microscopy (SEM) study reveals the morphology of pristine and annealed piezoceramics. It was found that NKN-NT (a lead free piezoceramic) being soft in nature induces more deformation and pop-in events were observed during load-displacement curve. The ratio of hardness to elastic modulus (>0.05) suggests more elastic recovery for pristine and annealed NKN-NT compared to PZT piezoceramic.